[nongnu] scratch/proof-general 73c13d63d9 2/3: Simplify code of `pg-protected-undo`

[Stefan Monnier]

branch: scratch/proof-general
commit 73c13d63d9c0dae5df00ade7cd8dfabef76fb11f
Author: Stefan Monnier <monnier@iro.umontreal.ca>
Commit: Stefan Monnier <monnier@iro.umontreal.ca>

    Simplify code of `pg-protected-undo`
    
    The last change made `undo-delta` be used at two places very close
    to each other, so consolidate the two calls.  Change the test
    order since in the case where `(eq last-command 'undo)` we ended up
    throwing away the work we'd just done and then returning the
    first element without checking that its delta is non-trivial.
    
    * generic/pg-user.el (pg--next-undo-delta): Rename from
    `pg--next-undo-elt`.  Make it check `last-command` at the beginning
    rather than at the end.  Make it return the delta rather than the elt.
    Don't bother special-casing `nil` and `(nil)`.
    (pg-protected-undo-1): Adjust accordingly.
---
 generic/pg-user.el | 44 ++++++++++++++++++++++----------------------
 1 file changed, 22 insertions(+), 22 deletions(-)

diff --git a/generic/pg-user.el b/generic/pg-user.el
index b47f770cab..e7a088d551 100644
--- a/generic/pg-user.el
+++ b/generic/pg-user.el
@@ -1569,7 +1569,7 @@ removed if it matches the last item in the ring."
 ;; `buffer-undo-list' in `proof-set-queue-endpoints'.
 ;;
 ;; Improved version due to Erik Martin-Dorel.  Uses auxiliary
-;; functions `pg-protected-undo-1' and `pg--next-undo-elt'
+;; functions `pg-protected-undo-1' and `pg--next-undo-delta'
 ;;
 
 (define-key proof-mode-map [remap undo] 'pg-protected-undo)
@@ -1621,7 +1621,7 @@ the locked region."
 (defun pg-protected-undo-1 (arg)
   "This function is intended to be called by `pg-protected-undo'.
 
-The flag ARG is passed to functions `undo' and `pg--next-undo-elt'.
+The flag ARG is passed to functions `undo' and `pg--next-undo-delta'.
 It should be a non-numeric value saying whether an undo-in-region
 behavior is expected."
 ;; Note that if ARG is non-nil, (> (region-end) (region-beginning)) must hold,
@@ -1630,11 +1630,10 @@ behavior is expected."
   (if (or (not proof-locked-span)
          (equal (proof-queue-or-locked-end) (point-min))) ; required test
       (undo arg)
-    (let* ((next (pg--next-undo-elt arg))
-          (delta (pg--undo-delta next))  ; can be '(0 . 0) if next is nil
+    (let* ((delta (pg--next-undo-delta arg))  ; can be '(0 . 0).
           (beg (car delta))
           (end (max beg (- beg (cdr delta))))) ; Key computation
-      (when (and next (> beg 0)                ; the "next undo elt" exists
+      (when (and (> beg 0)             ; the "next undo elt" exists
                 (> (proof-queue-or-locked-end) beg)
                 proof-strict-read-only ; edit freely doesn't retract
                 (not (and              ; neither does edit in comments
@@ -1649,24 +1648,25 @@ behavior is expected."
           "Cannot undo without retracting to the appropriate position")))
       (undo arg))))
 
-(defun pg--next-undo-elt (arg)
+(defun pg--next-undo-delta (arg)
   "Return the undo element that will be processed on next undo/redo.
-Assume the undo-in-region behavior will apply if ARG is non-nil."
-  (let ((undo-list (if arg             ; handle "undo in region"
-                      (undo-make-selective-list
-                       (region-beginning) (region-end)) ; can be '(nil)
-                    buffer-undo-list)))                 ; can be nil
-    (if (or (null undo-list) (equal undo-list (list nil)))
-       nil                             ; there is clearly no undo elt
-      (while (and undo-list             ; to ensure it will terminate
-                  (not (equal '(0 . 0) (pg--undo-delta (car undo-list)))))
-       (setq undo-list (cdr undo-list))) ; get the last undo record
-      (if (and (eq last-command 'undo)
-              (or (eq pending-undo-list t)
-                  (gethash undo-list undo-equiv-table)))
-         ;; then we are within a run of consecutive undo commands
-         (if (eq pending-undo-list t) nil (car pending-undo-list))
-       (car undo-list)))))
+Assume the `undo-in-region' behavior will apply if ARG is non-nil."
+  (let ((undo-list
+        (cond ((and (eq last-command 'undo)
+                    (or (eq pending-undo-list t)
+                        (gethash buffer-undo-list undo-equiv-table)))
+               ;; then we are within a run of consecutive undo commands
+               (if (eq pending-undo-list t) nil pending-undo-list))
+              (arg                     ; Handle "undo in region".
+               (undo-make-selective-list
+                (region-beginning) (region-end))) ; Can be '(nil).
+              (t buffer-undo-list)))              ; Can be nil.
+       (delta '(0 . 0)))
+    (while (and undo-list               ; To ensure it will terminate.
+                (not (equal delta
+                            (setq delta (pg--undo-delta (car undo-list))))))
+      (setq undo-list (cdr undo-list))) ; Get the last undo record.
+    delta))